Most food poisoning is caused by five groups of bacteria – Campylobacter, Salmonella, Clostridium, Listeria and Staphylococcus. Even small numbers of Salmonella cells can cause food poisoning but other types of bacteria have to be present in large numbers before they make food dangerous. In other words, they have been allowed to grow and multiply for a sufficiently long time to produce large numbers of cells.
If salmonella and Listeria are to cause problems, living cells of the bacteria have to be present in the food when it is eaten. Normal, but thorough, cooking should destroy these cells and render them harmless.
Staphylococci are different because they produce toxin (a poisonous chemical) when they are growing. Even though cooking may destroy the bacterial cells, it is unlikely to inactivate the toxin.
Food producers do their best to make sure that food is not contaminated with any food-poisoning organisms. But if some should be in food, the maintenance of a cold temperature can do a lot to minimize growth and therefore the risk of food poisoning.
The Food Hygiene (Amendment) Regulations 1990 require that, from April 1995, most short-life food must be kept at 5°C or colder after manufacture and throughout distribution and display. Keeping such a cold temperature required many food companies to buy better refrigeration equipment so, until April 1995, a temperature of no warmer than 8°C had to be maintained for those foods.
Although there is no law governing the performance of household refrigerators, you should use a thermometer to make your refrigerator is operating at 5°C or colder. Suitable thermometers are available in Sainsbury’s stores which sell freezer accessories.
Once food has cooled to 5°C or colder if any food poisoning bacteria are present most will grow only very slowly and it would take a long time for them to reach large enough numbers to cause a problem. But, if Listeria should be present, it will grow and multiply, even at refrigerator temperatures. And if the food is at 10°C, Listeria will grow more rapidly than any other organism.
Frozen foods are stored at -18°C throughout distribution and there is no possibility of bacterial cells growing and multiplying at that temperature.
But remember that neither chilling nor freezing kills all bacteria, so it is very important to keep chilled foods chilled and frozen foods frozen until they are used. Once they reach room temperature, bacteria become active again and food deterioration stars or resumes from where it left off.
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